The term solvent recovery generally refers to a process in which a liquid is separated, purified and reused as a solvent. Some typical solvent-recovery processes are:
(1) The recovery of solvents vaporized in the drying of synthetic fibers and films, plastics and rubber products, smokeless powder, impregnated fabrics, adhesives, printing inks, paints, lacquers, enamels and other organic coatings; PA1 (2) The recovery of solvents used in the solvent extraction of natural fats and oils or in other solid-liquid extractions; PA1 (3) The recovery of solvents used in the solvent refining of mineral or vegetable oils in other liquid-liquid extractions, in extractive and azeotropic distillations or in gas-absorption processes; PA1 (4) The recovery of solvents used for degreasing fabricated parts for dry cleaning or for other washing operations; and PA1 (5) The recovery of solvents used as mediums for chemical reactions or for the precipitation and crystallization of solids.
If an organic liquid is separated and purified, but not returned for reuse as a solvent, the operation cannot be strictly referred to as solvent recovery. However, except for the use to which the liquid is put, such operations may resemble solvent-recovery systems in every respect. Typical of such closely related processes are (1) the recovery of natural gasoline and light hydrocarbons from natural gas; (2) vapor recovery operations in petroleum refining; (3) the recovery of alcohol from fermentation gases; (4) the recovery of organic liquids from wood distillation and from coal tar distillation operations; and (5) the recovery of products or of unused reagents from chemical synthesis.
The growth of solvent-recovery systems has followed closely the growth of processes which manufacture and use organic solvents. While condensation of alcohol from vapor-laden air has been practiced since ancient times, some 99% of today's solvent recovery systems were put into operation after 1930. An excellent discussion of solvent recovery is found in Kirk-Othmer, Encyclopedia of Chemical Technology, Second Edition, Volume 18, pages 549-64 (1969), which is hereby incorporated by reference.